Neuronal damage in ischemia is initiated by excessive release of glutamate from brain nerve terminals. We have discovered, using novel rapid kinetic methodology developed in the P.l.'s laboratory, that certain substituted guanidines and related compounds are antagonists of calcium-dependent release of glutamate and dopamine from brain nerve terminals. One of these exhibits selective block of glutamate release. Such compounds, which we hypothesize to act as antagonists of presynaptic calcium-channels, may be employed as drugs to limit ischemic brain damage in stroke and traumatic brain injury patients. Our goal is to identify and synthesize additional substituted guanidine derivatives of improved potency and specificity for blockade of neurotransmitter release. To that end, we will employ molecular modeling tools and quantitative structure activity relationship analysis. Their mechanism of action and selectivity for antagonism of presynaptic calcium channels will be defined by electrophysiological, radioisotopic flux, and radioligand binding techniques. They will be tested for neuroprotective efficacy in animal models of stroke, both at Cambridge NeuroScience and in collaboration with investigators at the Massachusetts General Hospital and Cornell Medical Center. Our preliminary in vivo studies have demonstrated neuroprotection by substituted guanidines which block neurotransmitter release.